Interpretive Summary: There is growing evidence that consumption of plant-derived proteins rich in phytonutrients have beneficial effect in chronic diseases such as atherosclerosis, some forms of cancer and renal disease. In this study we report the effects of feeding diets containing either soy protein or flaxseed meal on lipid parameters in plasma and liver of obese diabetic rats. We used two phenotypes of SHR/N-cp rats in this study. Lean rats are hypertensive while obese rats show symptoms of type II diabetes and insulin resistence. We fed AIN 93 diets to all rats with different sources of protein. One group was fed 20 % of energy as casein, a second group was fed 20 % of energy as soy protein and a third group was fed 20 % of energy as flaxseed meal. In both phenotypes we observed that flaxseed meal significantly lowered plasma total cholesterol and triglycerides as compared to rats fed casein. Flaxseed meal also lowered lipid accumulation in livers of both phenotypes compared to rats fed casein. The marked lipid lowering effects of flaxseed meal indicate that it may be beneficial for humans with obesity, diabetes and lipid abnormalities. These data are helpful to other scientists, nutritionists, dietitians and food producing industry which process soybean and flaxseed.

Technical Abstract:
Soy protein and flaxseed meal have been reported to have beneficial effects on many chronic diseases in humans and animals. The primary objective of the study was to evaluate the beneficial effects of soy protein and flaxseed meal on hypertriglyceridemia and liver steatosis in obesity and diabetes. We compared the effects of dietary soy protein and flaxseed meal to that of casein on plasma and liver lipids in a genetic model of obesity, type II diabetes and insulin resistence namely the SHR/N-cp rat. Lean and obese phenotypes of SHR/-cp rats were fed AIN 93 diets containing 20% of energy from either casein (control), soy protein concentrate or flaxseed meal for six months. Plasma was analyzed for total cholesterol, LDL cholesterol, triglyceride and total protein. Liver was analyzed for steatosis by light microscopy after staining samples with Hematoxylin-Eosin and Oil-Red-O. Lean rats fed soy protein and flaxseed meal significantly decreased plasma total cholesterol (26.0% and 20.3% respectively) compared to rats fed casein. In obese rats only flaxseed meal had significant cholesterol lowering effect compared to control rats (41.3%). Soy protein but not flaxseed meal also significantly lowered both plasma LDL-cholesterol and HDL-cholesterol in lean phenotypes while in obese phenotypes only flaxseed meal significantly lowered LDL-cholesterol and HDL-cholesterol compared to casein-fed rats. Flaxseed meal also significantly lowered plasma triglyceride in both lean and obese rats compared to casein fed rats (33.7% and 37.0% respectively). There was significantly greater fat accumulation in livers of obese rats than lean rats (200%) regardless of type of dietary protein. Flaxseed meal significantly lowered fat deposition in livers of both lean and obese rats compared to rats fed casein or soy protein. The nature of dietary component(s) present in flaxseed meal or soy protein responsible for hypolipidemic effects is not clear. The marked hypotriglyceridemic and hypocholesterolemic effects of flaxseed meal may have important therapeutic implications in patients with hypertriglyceridemia and hypercholesterolemia and deserve further study in humans with these disorders. Flaxseed meal supplementation may provide a new therapeutic strategy to reduce hypertriglyceridemia and fatty liver.